Variable impedance assembly



Jan. 26, 1960 Filed March 8, 1956 F. P. VACHA VARIABLE IMPEDANCE ASSEMBLY 2 Sheets-Sheet 1 Fig.2

76 INVENTOR. FRED P. ACHA Ma Q ATTORNEYS Jan. 26, 1960 2F. P. VACHA VARIABLE IMPEDANCE ASSEMBLY Filed March 8, 1956 2 Sheets-Sheet 2 Fig. 7

| l l I I IN V EN TOR.

Fig. 9

FRED P. VACHA ATTORNEYS 2,922,973 7 VARIABLE IMPEDANCE ASSEMBLY Fred P. Vacha, Babson Park, Mass assignor to The Gamewell Company, Newton Upper Falls, Mass, a corporation of Massachusetts The present invention relates generally to variable impedance assemblies, and more particularly to a novel assembly for making connections from fixed points on an impedance to terminals for external electrical connection therewith.

It is a primary object of the present invention to provide an assembly having means for making low impedance connections from conveniently accessible terminals to fixed points on a potentiometer, rheostat or other variable impedance element. Such fixed connections are exemplified by the two end terminals of a potentiometer, and it will be obvious that similar considerations apply to a tap terminal; that is, a terminal connected to a fixed point on the impedance intermediate the end terminals.

There are a great many forms of assembly for variable impedances in current use. The varied techniques of manufacture depend upon a wide range of requirements relating to environment, range of impedance values, resolution tolerances, precision of impedance values, and other specifications. However, the art of manufacturing variable impedance elements having extreme precision coupled with low resolution error and great freedom from environment factors such as temperature, humidity and vibration, is relatively new. In more recent control circuit applications for potentiometers and the like, the further requirement of miniaturization has been superimposed upon the others, with the result that many longestablished practices of fabrication have had to be discarded and new practices developed. In fact, at the present time there are 'many applications for potentiometers in which the environmental conditions are more severe than those hitherto encountered in the art, It is in any case essential that the mode of construction be expressly adapted to the specific conditions of use.

In this context, a further object of this invention is to provide a potentiometer adaptedfor miniaturization, and provided'with means for making fixed connections having extremely .low impedance, said connections beingsubstan tially independent of the effects of vibration and temperature variations.

A still further object is to provide means for making end connections on a toroidal impedance winding in very close physical relationship, whereby the wiper contact moves but a small angle in rotating from one end terminal connection to the other. With the foregoing and other objects in view, a feature of this invention resides in the provision of spring contact terminal lead-in wires including coiled or bent portions, the wires bearing resiliently upon the impedance element without the aid of soldering", brazing or welding.

Another feature'resides in an assembly for a variable impedance that combines simplicity of construction and adaptability to the use of coiled or bent spring contact wires of the above type.

Other features of the invention reside in certain features of construction and modes of assembly that will be more readily understood from the following description 2,922,973 Patented Jan. 26, 196i) thereof, and from the appended drawings illustrating the same, wherein:

Fig. 1 is an end elevation of a potentiometer embodying one form of the invention;

Fig. 2 is a longitudinal elevation taken on line 2-2 of Fig. 1;

Fig. 3 is a plan view taken on line 3-3 of Fig. 1;

Fig. 4 is an oblique view showing the underside of the terminal block of Fig. 1 with assembled spring contact wires;

Fig. 5 is a longitudinal elevation in section of an end terminal;

Fig. 6 is an end elevation of a second embodiment of the invention;

Fig. 7 is a side elevation in section of the embodiment of Fig. 6;

Fig. 8 is a plan view of the embodiment of Figs. 6 and 7, with the terminal block removed;

Fig. 9 is an elevation in section of one of the end terminals in Fig. 6; and

Fig. 10 is an oblique view of the underside of the terminal block of Fig. 6 with spring contact wires assembled thereon.

Referring to Figs. 1 to 5, there is shown a metallic housing 12 having a cyindrical flange-like portion 14 and a portion 16 of smaller diameter adapted to be received through a mounting hole in a suitable chassis. The portion 16 has outside threads 18 to receive suitable washers and a mounting nut.

The portion 14 of the housing has bores of progressively increasing diameter, thereby forming shoulders 20 and 22. A generally rectangular opening 24 is provided in the housing intermediate the shoulders 29 and 22, as shown particularly in Figs. 2 and 3.

An insulating locator or guide ring 26 is fitted within the housing and against the shoulder 20 as shown in Fig. 2. This ring is of circular shape, and has the crosssection illustrated in the lower part of Fig. 2 except in the region adjacent the terminals, in which region it is provided with an elongated slot 28 and two shorter slots 30 and 32 spaced therefrom.

A cylindrical insulating insert 34 having a wide rectangular slot 36 is received within the housing, with a portion of the ring'26 fittingly underlying itsinner surface and with the slot 36 symmetrically overlying the narrower slots 30 and 32 in the ring 26.

A circular mandrel 38 having a toroidal winding 40 of resistance wire wrapped thereon is received within the insert 34 and against the end of the guide ring 26, in which position it may be held by any suitable means such as varnish, glue, cement or other means suited to the intended conditions of use.

The rotating parts of the potentiometer may be of any desired form since the invention is not concerned therewith. In the drawings, there is shown for illustration a sintered bronze rotor bushing 42 received in one end of the housing, and a rotor shaft 44 received in the bushing and extended to the impedance, the shaft being coaxial therewith. An insulating bushing 46 isreceived over the end of the shaft, and a collector ring 48 is received over the bushing. The collector ring has a flange lying Within the toroidal winding, this flange having a wiper arm 50 of resilient metal strip secured thereto by spot welding or the like. The'arm 50 has a short piece of wire forming a wiper contact 52 welded adjacent its end portion. The wiper contact bears resiliently upon the toroidal winding.

Connections from the winding to the external circuit are made through two end terminals 54 and 56 and a variable terminal 58. Each of these terminals has an accurate bore 59- as shown in Fig. 5, and is staked as indicated at '62 to a curved insulating terminal block 64. The

block 64 is fittin'gly received over the opening 24 in the i Lthe terminal 58, whichis then crimped over the wire substantially as indicated at 70 on the terminal 54. As

' -shown in Fig. l, the elongated'slot 28 in the ring 26 is not radial to the housing, but guides the wire so that it may Tbear resiliently upon the collector ring 48. i

The end connections to the impedance winding are made through shorter coiled spring contact wires 72 and 74, each received in a bore 59 with only such slight clear- :ance as is necessary for insertion. Theterminals may also be crimped about the wires as indicated at 70. If "desired, the wires and terminals may be soldered as indicated at 75. V Each of the wires 72 and 74 has a pair of right angle bends 76 and an intermediate semi-circular bent portion 78. The straight portions of the wires received within their respective terminals are aligned with the corresponding portion of the wire 68 as viewed in' Fig. 3, and the arcuate bent portions provide a displacement -to bring the lower straight portions of the wires 72 and 74 approximately to the slots 30 and 32 in the ring 26. It

.will be observed that while the insert 34 overlies a portion of the elongated slot 28, thus restraining the wire 68 at its inner end, the wide slot 36 in the insert exposes the slots 30 and-32 entirely. The wires 72 and 74 are I 4 128 bearing a wiper 130 is secured by welding or other suitable means to the flange 126. The brush wire 131 is crimped to the terminal 94 and bears resiliently upon the collector ring 124.

End contact wires 132 and 134 of appreciably smaller diameter than the holes 108' and 110 are crimped in a similar way within the terminals 90 and 92, as fully illustrated in Fig. 9. These wires each have two straight portions and an intermediatebent portionbetween right angle bends, the shapes of these bent portions being fully shown in Figs. 8, '9 and 10. The bent portions are situated immediately beneath the terminals in the space provided by the opening 100 in the body 88. The contacts bear resiliently upon the impedance near the ends 118, and are as close together as permitted by the voltage to be applied. Thus the end'connections to the impedance subtend a very small arc.

" The function of the holes 108 and 110 in the locator 104 is to assist in locating the contact wiresv on the impedance 114-when the latter is in its assembled position,

and to locate the wires as close together on the impedance as possible. Thus, assuming the terminal block is secured by screws onto the body 88 with the contact wires 132 and 134 secured in their respective terminals,

insertion of-the impedance 114 into positioncauses the wires to be rotated counterclockwise and clockwise respectively into the corners provided between the impedreceived through the latter slots and bear resiliently upon V the toroidal winding as indicated in Figs. 2 and 3.

. 7 It will be observed that the plane of the semi-circular portion 78 of each of the wires 72 and 74 lies within the space provided by the opening 24 in the housing be .tween the insulating terminal block and the overlapped insulating ring 26 and insert 34. Also, these arcuate portions of the wires are so oriented as to increase the resiliency thereof, whereby the required bearing pressures can be attained and controlled with considerable accuracy. tacts are Wholly dependent upon the bearing pressure, as no soldering, brazing or welding of the wires to the winding is employed. This bearing pressure is very high,

being in excess of 10,000 p.s.i., and the contact resistance 7 is correspondingly substantially negligible. The arcuate portions of the Wires lie generally in planes parallel with the direction of the bearing force of the wires on the impedance. This bearing force is of course preferably precisely normal or perpendicular to the surface of the impedance so as to avoid the possibility of the wires being jarred and slipping in relation to the impedance.

- Figs. 6 to 10 show a second embodiment of the invention having the further feature of end connections in very close relationship. There is provided a generally cylindrical metal housing 88 adapted to support the rotor shaft. A pair of end terminals 90 and 92 and a brush terminal 94 are supported on a curved insulating terminal block 96 secured by screws 98 onto the body 88 over an opening 100 therein. The terminals are spun onto the terminal block as indicated at 102 in Fig. 9, and each terminal has a central bore to receive a contact wire.

A- generally cylindrical insulating locating ring 104 having three transverse holes 106, 108 and 110 is inserted fittingly within the body 88 and rests against a shoulder 112 therein. The holes are located beneath an opening 100 in the body 88 as shown in Fig. 8. A toroidally-w'ound impedance element 114 is inserted within the locator 104 and rests against a shoulder 116 therein. Suitable means such as glue, varnish, cement or other It will be appreciated that the electrical conance and the holes 108 and 110, as shown in Fig. 8.

It will be observed that the precision of the spacing between of the wires 132 and 134 is determined by the holes 108 and '110, and more particularly by the adjacent walls thereof against which the wires are held by the impedance. 7 From the foregoing description, it will be appreciated that a desirable variable impedance assembly has been provided, in which the various parts are of simple form and readily assembled. The. assembly includes the desirable features of fixed connections provided by low impedance spring contact lead-in wires bearing resiliently and firmly with controlled pressure on the impedance, without the aid of techniques involving the fusion of dissimilar metals. Thus the difliculties often encountered with such fusing techniques due to various environmental conditions are entirely avoided. There is further provided a mode of construction and assembly particularly well adapted to the provision of coiled or bent portions on the spring contact wires to increase their resiliency and to aid in the attainment of the desired bearing force of the wires upon the impedance winding. And also, the inyention is well adapted to provide a minimum distance between the end connections to the impedance.

While the invention has been described with reference to two specific embodiments thereof, it will be appreciated that it is not limited thereto; but rather, such modi fications thereof in design and structure as would occur i ,to one skilled in the art upon a reading of the foregoing means are used to secure the impedance in the position description -are also within the spirit and scope of the invention. v

Having thus described the invention, I claim:

. 1. A variable impedance assembly having, in combi-' nation; a metal body having a first opening in a wall thereof, an insulating member having a second opening .therethrough supported within the body with the second opening underlying the first opening, an impedance element insulatedly supp'orted within said body, an insulating terminal block supported by the body over'said first opening, a metal terminal supported by the terminal block, and a spring contactwire having a pair of right angle bends, a curved portion intermediate said bends and a pair of substantially parallel portions normal to said curved portion, one ofsaid substantially parallel portions being secured to the terminal, the other portion being guided by said second opening and bearing resiliently on the impedance and said curved portion being unsupported and lying entirely within the space defined by said first opening.

2. The combination according to claim 1 in which the substantially parallel portions of the contact wire are straight.

3. A variable impedance assembly having, in combination, a metal body having an extended flange-like portion with a first opening in a wall thereof, an insula-ting guide member fittingly received within said flange-like portion and having a slot in the edge thereof underlying said first opening, an impedance element insulatedly supported within said body, an insulating terminal block supported by the body over said first opening, a metal terminal supported by the terminal block, and a spring contact wire having a pair of right angle bends, a curved portion intermediate said bends and a pair of substantially parallel portions normal to said curved portion, one of said substantially parallel portions being secured to the terminal, the other portion being guided by said slot and bearing resiliently on the impedance and said curved portion being unsupported and lying entirely within the space defined by said first opening.

4. The combination according to claim 3 in which the bearing force of the wire on the impedance lies in the plane of the curved portion of the wire and the slot restrains the wire circumferentially of the impedance but allows clearance for flexure of the wire in the direction of said force.

5. A variable impedance assembly having, in combi nation, a metal body having a generally cylindrical portion with a first opening in the wall thereof, an insulating guide ring fittingly received within said cylindrical portion and having a slot in an edge thereof underlying said first opening and extending parallel to the axis of said cylindrical portion, a cylindrical insulating sleeve fit tingly received in said body in position to close the open end of said slot, an impedance element insulatedly supported within said body, an insulating terminal block secured to the body over said first opening, a metal terminal secured to the terminal block, and a spring contact wire having a pair of right angle bends, a curved portion intermediate said bends and a pair of substantially parallel portions normal to said curved portion, one of said substantially parallel portions being secured to the terminal, the other portion being guided by said slot and bearing resiliently on the impedance and said curved portion being unsupported and lying entirely within the space defined by said first opening.

6. A variable impedance assembly having, in combination, a metal body having a first opening in a wall thereof, an insulating member having a hole therethrough supported within the body with said hole underlying said first opening, an impedance element insulatedly supported within said body, an insulating terminal block secured to the body over said first opening, a metal terminal supported by the terminal block, and a spring contact wire having a pair of right angle bends, a curved portion intermediate said bends and a pair of substantially parallel portions normal to said curved portion, one of said substantially parallel portions being secured to the terminal, the other portion being guided by said hole and bearing resiliently on the impedance and said curved portion being unsupported and lying entirely within the space defined by said first opening, said wire being of appreciably smaller diameter than said hole and being urged thereagainst by said impedance, said hole being positioned to restrain said wire transversely of its bearing force on said impedance but to allow flexure of the wire in the direction of said force.

7. A variable impedance assembly having, in combination, a metal body having a first opening in a wall thereof, an insulating member having a pair of closelyspaced holes therethrough supported within the body with said holes underlying said first opening, an impedance element insulatedly supported Within said body, an insulating terminal block secured to the body over said first opening, a pair of metal terminals supported by the terminal block, and a pair of spring contact wires, each wire having a pair of right angle bends, a curved portion intermediate said bends and a pair of substantially parallel portions normal to said curved portion, one of said substantially parallel portions being secured to one of said terminals, the other portion being guided by one of said holes and bearing resiliently on the impedance and said curved portion being unsupported and lying entirely within the space defined by said first opening, each of said wires being appreciably smaller in diameter than the hole in which it is guided and being urged thereagainst by said impedance.

8. The combination according to claim 7, in which the impedance forces the Wires against the adjacent edges of the holes.

References Cited in the file of this patent UNITED STATES PATENTS 1,947,437 Schellenger Feb. 13, 1934 2,570,968 Muller Oct. 9, 1951 2,644,064 Jack et a1 June 30, 1953 2,657,295 Barclay Oct. 27, 1953 2,782,288 Weld Feb. 19, 1957 

